From U.S. Pat. No. 3,718,160 there is known a stabilizer comprising a chamber consisting of a deformable bladder, a seat supporting such chamber with an orifice allowing the air to pass into or out of the chamber and means making it possible to fit this seat to the ventilation shaft so that the orifice is directed upstream, the respective dimensions of the chamber and section of the shaft being such that under the action of pressure differences upstream and downstream, the variations in volume of the chamber that result therefrom modify the air passage section in the space between the chamber and shaft. In comparison with those previously known, this stabilizer has the advantage of stabilizing the air delivery without amplifying sudden fluctuations and consequently without maintaining oscillations in the shaft.
According to an embodiment of this stabilizer, described in U.S. Pat. No. 3,718,160, the chamber consisting of a bladder is made of a moldable or injectable flexible and elastic material such as rubber or the like. Naturally the bladder is molded in such a shape that, at rest, it occupies minimal volume, its own elasticity assuring its return to this minimal volume as there is a decrease in the pressure difference between the zones located upstream and downstream in the shaft from the stabilizer. This arrangement has the double drawback of being onerous and not durable because of the reduction of elasticity of the bladder material as it ages.